Bovine uterine estrogen (E) and progesterone (P) receptor proteins will be purified with the new disulfide affinity chromatography system. Work with affinity labeling perturbation of 20 beta-hydroxysteroid dehydrogenase will be continued to establish macromolecular conformational analysis techniques, which will ultimately be applied to E and P receptor proteins. New affinity labeling progesterone and estrogen derivatives will be synthesized and tested for biological activity in the rat; and also used as steroid binding probes in our study of the nature of interaction between the substrate and steroid binding site. The mechanism whereby cystamine preserves E-receptor activity will be further investigated to determine whether it implies that some chemical transformation (intra or intermolecular) of the receptor is integrated with its role in mediating steroid hormone action.